1. Field of the Invention
The present invention relates to an image forming apparatus, such as a laser printer, a digital copying machine or a facsimile apparatus.
2. Description of the Related Art
In an image forming apparatus, such as a laser printer or a digital copying machine, a dither method, a density pattern method, an error diffusion method, or the like is generally used as a recording method designed to improve the quality of halftone images.
Although such a recording method allows proper reproduction of halftones, it is accompanied by inconveniences, e.g., a decrease in resolution, the generation of a moire, the generation of textures, and the generation of rugged portions at oblique lines or curved lines.
In an image forming apparatus using laser exposure, a scheme based on pulse width modulation has been studied to compensate for these drawbacks. In this scheme, the radiation time of a laser beam within one pixel is controlled by an area gradation method. U.S. Pat. No. 4,626,923 (Yoshida), for example, discloses such a scheme.
Even in this case, however, since the radiation time of a laser beam is modulated with a pulse width, cracks in an image or halftones cannot be smoothly expressed, resulting in poor image quality.
That is, such modulation of the radiation time of a laser beam with a pulse width causes the problem that an image is partially omitted or halftones cannot be smoothly expressed.